Hydrogenation reactions are typically highly exothermic, and as such, care must be taken in order to control reaction temperatures so that proper reaction conditions are maintained and desired reaction products are obtained. On a commercial scale, this may typically be done by utilizing a reactor that facilitates heat removal. Tubular reactors, fluidized bed reactors and jacketed, stirred tanks are all examples of reactors whose design allows for the circulation of coolant, typically in a jacket external to the reactor. While effective at heat management, each of these requires the expenditure of additional resources in order to maintain isothermal conditions within the reactor.
Solvents may also be utilized to manage heat generated by exothermic hydrogenation reactions, and in particular, water has been utilized for this purpose. However, the addition of water into such reactions can be undesirable in that it typically must be removed to provide commercially acceptable end products, adding cost and time to the process. Additionally, extraneous water can decrease the activity of any catalyst desirably used in the process, in some cases, can even contribute to catalyst degradation, and may actually slow reaction times.
One commercially important example of a hydrogenation reaction involves the conversion of glycerin to provide a distribution of glycols including, e.g., 1,2-propanediol, 1,3-propanediol, 1,2-ethanediol, etc. In the conventional process, glycerin and hydrogen or a hydrogen-containing gas are heated to a reaction temperature in the presence of a catalyst, most typically a copper containing catalyst. Such conventional processes, unfortunately, can provide suboptimal productivity.
Firstly, low activity and poor catalyst lifetime can limit the productivity of conventional catalysts for this particular hydrogenation reaction. Also, and although, e.g., 1,2-propanediol may be the desired end product, the formation of other glycols, such as 1,3-propanediol, 1,2-ethanediol and other by-products can increase under certain reaction conditions, such as a wide variation in temperature, the presence of excess water, the low selectivity of some conventional copper containing catalysts or the use of lower grade reactants, etc. Reaction selectivity may be influenced to favor production of a particular product, or disfavor production of reaction by-products, by adjustment of one or more reaction conditions, although such adjustment typically does not come without expense. And, less desirable glycols and/or typical reaction by-products, e.g., hexanediol and propylene glycol propionates, can be difficult, if not impossible, to remove by distillation techniques.
Desirably then, an improved hydrogenation process would be provided in which heat could be adequately managed without the addition of substantial amounts of water. Effective heat management should prevent substantial degradation in catalyst activity or selectivity. Further advantage could be seen if the process were economically practical, or even advantageous, by the productive utilization of the energy of reaction generated thereby. Applicability of the process to a variety of grades of starting materials would further enhance the commercial significance thereof, as would utilization of catalysts having a longer lifetime and capable of exhibiting a higher activity and/or selectivity for the desired reaction products than catalysts conventionally utilized in this process.